Using-SyncUpdateDC-to-Reduce-Screen-Flicker.md

@@ -8,6 +8,34 @@ Table of Contents
 
 ## Overview
 
+In the development of a GUI app, we often need to update an area on the
+screen multiple times just for a user input. For example, if the user
+presses the up and down keys, the highlighted item in the list box will
+change. At this point, the program should perform the following operations:
+
+1. Erase the original highlighted item with the background color of
+   a normal item;
+1. Draw the text of the original highlighted item with the foreground
+   color of the normal item;
+1. Erase the new highlighted item with the background color of the
+   highlighted item;
+1. Draw the text of the new highlighted item with the foreground color
+   of the highlighted item.
+
+This frequent drawing will cause the screen to flicker if we don't do
+any special processing.
+
+Generally, we can use one of the following ways to eliminate this flicker:
+
+1. Create a memory DC and draw content to the memory DC first, then
+   call `BitBlt` to blit the content to screen.
+1. Use MiniGUI's double buffer main window. This is essentially the
+   same as the first method.
+1. Use the new synchronous update mechanism introduced in MiniGUI 3.2.x.
+
+This documents describes how to the synchronous update mechanism to
+reduce screen flicker.
+
 ## Usage
 
 - Including option `--enable-syncupdate` when configuring MiniGUI.
@@ -31,3 +59,4 @@ the screen flicker. However, it has the following restrictions:
 Therefore, for modern graphics stack (system shipped with a GPU),
 the better way is using off-screen surface and exploiting the
 hardware acceleration as far as possible.
+